Rails - Jul 2008 - calculations on nested resources

Hi,

I can''t seem to find a solution to the folowing problem.
I have 3 resources that are all bound to eachother like this:

class Item < ActiveRecord::Base
  belongs_to :item_category
  // has a date and amount attr
end

class ItemCategory < ActiveRecord::Base
  has_many :items
  has_many :item_tops
  // groups the items in categories
end

class ItemTop < ActiveRecord::Base
  belongs_to :item_category
  // has a start and stop date and an amount attr
end

The thing I would like to do now starts from the ItemTop resource. When
I do a search, it will search for all ItemTop resources where the start
and stop dates are between or equal to 2 dates the user inserted in the
search box.

The result of the search must contain the following data:
the ItemTop amount and the ItemCategory it reflects upon (this I have so
far).

But next, it must show the total sum of the amounts of the Item
resources where the Item.date also resigns between the 2 dates the user
added. I have no idea how I can get this implemented in clean Ruby
style.

I hope someone can help me out with this.

Thank you in advance
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I don''t want to come over like a lazy person that just want someone
else
to write the code for him. I know a way, but it is not the best idea due 
to performance issues.

The way I''m working now it to define the following method in my model:

  def actual
    total = BigDecimal.new("0")
    item_category.items.each do |set|
      if set.set_date >= start_date && set.set_date <= stop_date
        total += set.amount
      end
    end
    return total
  end

It gets the job done, but it iterates over every item. Is there a way to 
solve this by just retrieve the good items from the database instead of 
all the items?
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On 12 Jul 2008, at 18:55, Michael Rigart wrote:
>
> I don''t want to come over like a lazy person that just want
someone
> else
> to write the code for him. I know a way, but it is not the best idea  
> due
> to performance issues.
>
> The way I''m working now it to define the following method in my
model:
>
>  def actual
>    total = BigDecimal.new("0")
>    item_category.items.each do |set|
>      if set.set_date >= start_date && set.set_date <=
stop_date
>        total += set.amount
>      end
>    end
Something like
item_category.items.sum :amount, :conditions => ...
?
Fred 

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Frederick Cheung wrote:
> On 12 Jul 2008, at 18:55, Michael Rigart wrote:
> 
>>    total = BigDecimal.new("0")
>>    item_category.items.each do |set|
>>      if set.set_date >= start_date && set.set_date <=
stop_date
>>        total += set.amount
>>      end
>>    end
> 
> Something like
> item_category.items.sum :amount, :conditions => ...
> ?
> Fred
Well I''ll be damned Fred. I didn''t know that this was even
possible in
Rails.
Looks like I need more reading :)

Thank you for the help

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